The invention generally relates to the packaging of semiconductor chips, and more particularly to inhibiting damage to semiconductor chip packaging structures during package molding.
The fabrication of packaged semiconductor chips or dies is well known. One conventional ball grid array (BGA) packaging method includes affixing a fabricated die to a substrate and electrically connecting the die to conductive leads on the substrate. The electrical connection may be through wire bonding or other known connection techniques which couples bond pads on the die to corresponding leads on the substrate. A plastic molding material is then typically applied to the die and substrate for encapsulating the die on the substrate. Exposed contacts on the substrate connected to the conductive leads are used to electrically connect the packaged die to a circuit board. The molding material is typically applied by placing the die and substrate in a mold and injecting molding material over the die and substrate and exerting a force by way of a mold clamping mechanism.
A recurrent problem associated with the molding process is that the force applied to the substrate during molding is often greater than the ability of the substrate to resist compression, and thus the force exerted on the die and substrate often damages the delicate wiring and/or the contacts on the substrate, thereby destroying the viability of the packaged product. Further, the compressive forces encountered during molding may cause distortion of the substrate which in turn causes the plastic encapsulation material to leak onto undesired areas of the substrate, producing a defective package for the die.
A conventionally fabricated BGA semiconductor die package 10 is shown in FIGS. 1-3. The package 10 includes a die carrier 12 which includes an interposer layer or substrate 14 and a first solder mask layer 16, which isolates areas of the substrate 14 that are to be bonded to a die 18 supported by the carrier 12. The substrate 14 has a trench 25 (FIGS. 2-3) to allow conductive leads 34 formed on the substrate 14 to interconnect with bond pads 47 on the die 18. These conductive leads 34 are connected with conductive traces on the substrate 14, which in turn connect with external contacts 28. The die 18 is positioned on a surface of the first solder resist layer 16 and has bond pads 47 which connect with respective conductive leads 34 through conductively lined holes 45 provided in the solder mask 16. The die carrier 12 is diced from a carrier strip, which may include up to twelve separable die carriers. Alternatively, the die carrier may be diced from a carrier matrix, which may include numerous rows and columns of separable die carriers.
Most substrates 14 are formed of either a glass weave reinforced resin or a tape. A second solder mask 20 is provided on a surface 15 of the substrate 14, leaving exposed the contacts 28 and shielding the conductive leads 34 running along the surface 15 from the contacts 28 to the centrally-located trench 25. Specifically, located on a surface 15 of the substrate 14 and exposed by openings within the second solder mask layer 20 are the plurality of contacts 28 which will have solder balls screen printed thereon for use in connecting the die package 10, after package molding, to a printed circuit board. Wiring in the form of the conductive leads 34 is shown extending into the trench 25 to contacts 45 provided in holes in the first solder mask layer 16 to bond pads 47 of the die 18. Some of the contacts 28 may be formed as openings, such as openings 30 extending through the substrate 14. After molding, a mold material strip 24 fills the trench 25 on one side of the substrate 14 and provides protection to the wiring 34 extending into the trench 25 to the die 18. The mold material 24 also covers the die 18 and extends slightly outwardly thereof onto the substrate 14. The mold material 24 is only partly shown in FIG. 2 for clarity of illustration.
When a mold material, such as the mold material 24 (FIGS. 1-3), is applied to the die 18, the substrate 14, and both solder resist layers 16, 20 by injection into a mold cavity, a force is exerted on the surface 19 of the die 18. This causes a compressive force to be exerted down on the substrate 14 squeezing together its opposite surfaces. These compressive forces may destroy the wiring 34 on each surface of the substrate 14, rendering the packaged product useless. Further, these compressive forces may also cause the mold material strip 24 to weep over the solder mask 20, creating an undesirable mold material mass 26 (FIG. 1) which may cover one or more of the contacts 28, again rendering the packaged product useless.
In one aspect, the invention provides a semiconductor die carrier which includes a substrate which has greater resistance to compressive forces. The substrate includes holes extending therethrough which are filled with a material which has a greater resistance to compressive forces than the substrate itself, thereby reducing the possibility of a defective product being produced by compression of the substrate during package molding.
In another aspect, the invention further provides a method of fabricating a semiconductor die package. The method includes forming a substrate having a plurality of holes extending therethrough, filling the plurality of holes with a material which has a greater resistance to compressive forces than the substrate, attaching a die to the substrate, and encapsulating the die and a portion of the substrate with a mold material.